The erosion of soil on the earth continues to occur as rain and flood waters run from high elevations to lower elevations. Many efforts have been made to reduce the erosion of soil by interrupting the runoff of water, or at least slow down the water flow and thereby reduce the extent of erosion. Erosion control blocks are available for covering watershed areas to protect the underlying soil from being carried with the runoff water. Many styles, shapes and sizes of erosion control blocks are available for placement together to form a mat that covers the ground to be protected from erosion. The use of erosion control blocks is preferred over the use of a slab of concrete, as concrete can crack and settle if the underlying ground is unstable, which it is in many watershed areas. It is also difficult to make a concrete slab that is adapted to slow down the velocity of water that flows thereover. Erosion control blocks of the articulating type continue to conform to the contour of the ground, even when the ground contour changes.
Blocks that are simply placed side by side on the ground are helpful in reducing soil erosion, but only in situations where the velocity of the runoff water is low or moderate. Otherwise, the hydraulic lift of the flowing water can cause the blocks to actually lift off the ground and be carried or otherwise moved so that the erosion protection is compromised. Of course, the heavier the block the less likely it is to be moved by high velocity water currents. This solution is costly and often prevents the installation of the heavy blocks by persons who must lift each block and place it into position with others to form the mat.
More recently, erosion control blocks have been constructed so as to be laterally interlocking so that horizontal movement is prevented. U.S. Pat. No. 5,556,228 by Smith is an example of a commercially accepted interlocking erosion control block that articulates to conform to the contour of the ground. Such type of block has been accepted by governmental organizations for use on large waterways to halt erosion of the same.
In order to further enhance the stability of a revetment block or erosion control block, holes can be formed through the body of the block so that vegetation can grow therethrough and anchor the block to the underlying ground. The use of vegetation to anchor the block or mat of blocks to the ground is advantageous in situations where the mat of blocks is not constantly covered by a substantial depth of water, as vegetation does not grow well under such conditions. Rather, there are many water shed areas where the mat of blocks covers areas that are not under water, but are subjected to substantial water flows during rains and the like. Water ways and other watershed areas comprise such situations, which may be generally dry, but which can carry heavy flows of fast moving water during storms and flood conditions. The interlocking nature of the erosion control blocks together with the anchoring of the same to the ground by vegetation allows the erosion of the underlying ground to be controlled.
While the vegetation holes in erosion control blocks allows anchoring thereof by vegetation, such holes can also present a disadvantage. For example, if vegetation does not fully occupy the opening in the block, or if there is no vegetation at all, then the hole in the block can function as a small barrier to the flow of water over the block, and impart a hydraulic lifting force on the block. In other words, the water flowing over the block applies a force to the downstream side of the hole. The resulting water turbulence and the hydraulic forces can impart a force on the block that tends to lift the upstream portion of the block. If the upstream side of the block starts to lift and becomes separated from the ground, then the lifting forces avalanche and can be sufficient to completely lift the entire block from the mat. If this occurs, then the surrounding blocks are more easily dislodged from the mat, whereupon the integrity of the entire mat of blocks can be compromised. If the mat of blocks is installed on a slope that is to be protected from erosion, such as a flume, then the velocity of the water is accelerated due to the downhill grade. With an increased velocity of a large volume of water, the integrity of the mat of blocks must be maintained.
Often the erosion control blocks are installed by workmen who can carry one block with a hand, from a skid of blocks to the location where the mat is to be formed. To that end, the blocks must be of a weight that allows an average workman to conveniently carry a block, and the block must be constructed to allow easy gripping of the same with one hand. An average four-inch thick concrete block of the type described above in U.S. Pat. No. 5,556,228 can weigh about 56 pounds, and can be carried with one hand a distance sufficient to install the same in a watershed area. An eight-inch block of the same configuration can weigh about 115 pounds, and can also be carried by a workman with two hands from a skid to the site of installment. Because of the weight, workers generally grasp the arms of the block using two hands. If the blocks are too heavy, they must be carried by wheeled carts or otherwise in order to transport them at the work site.
Facilities exist for testing the hydraulic stability of erosion control blocks in order to enable the manufacturer to certify that the blocks can remain stable under specified water flow conditions. Often such certifications are necessary in order for block suppliers and manufacturers to be granted contracts for erosion control projects. These facilities can place the test blocks under actual working conditions in a laboratory setting, where the grade, water depth, volume and velocity can be accurately controlled. As an alternative, blocks can be made physically very large and heavy to assure that they will not be moved under the severest water flow conditions. Such overkill renders the blocks unnecessarily large, heavy and difficult to install. However, once the hydraulic stability characteristics of a block are understood, they can be used in engineering the design of an efficient block that conforms to specified constraints, is easy to handle and install and is cost effective.
From the foregoing, it can be seen that a need exists for an interlocking erosion control block that employs an efficient system of vegetation holes therein. Another need exists for an erosion control blocks which employs vegetation holes therein at locations that allow easy grasping of the same by a workman. Yet another need exists for an interlocking erosion control block having plural vegetation holes placed at locations to afford sufficient area for vegetation growth, to allow easy grasping of the block, but not at locations that would affect the structural integrity of the block.